Usefulness of Measurement of Serum Iodine Level to Assess the Appropriate Low Iodine Diet Preparation / 대한갑상선학회지

ABSTRACT

BACKGROUND AND OBJECTIVES: Low-iodine diet (LID) is generally recommended prior to radioactive iodine (RAI) therapy to increase RAI uptake. Recently, we suggested spot urine iodine/creatinine (I/Cr) ratio as a good alternative method replacing measurement of 24 hr urine iodine excretion for the evaluation of appropriate LID preparation. In next step, we studied to evaluate the usefulness of serum iodine concentration comparing with urine iodine concentration and urine I/Cr ratio to assess LID preparation status. MATERIALS AND METHODS: We prospectively measured serum iodine concentration, spot urine iodine concentration, and urine I/Cr ratio in 419 patients with differentiated thyroid carcinoma undergoing LID. Appropriate LID preparation was defined as urine I/Cr ratio less than 66.2 ug/gCr. RESULTS: There were significant correlations between serum iodine and the spot urine iodine concentrations or urine I/Cr ratio; the correlation coefficient was 0.51 for urine iodine concentration and 0.62 for I/Cr ratio (p<0.001). Calculated R2 after log-log transformation was 0.45 for I/Cr ratio. The cutoff value of serum iodine concentration was 20.4 ug/L (sensitivity 79.3%, specificity 81.5%) for the evaluation of appropriate LID. CONCLUSION: Measurement of serum iodine concentration may be useful as an adjunct parameter for assessing LID preparation, but its sensitivity and specificity were relatively low compared to the urine I/Cr ratio.